1. Field of Inventions
The present inventions relate generally to devices for performing therapeutic operations on body tissue.
2. Description of the Related Art
There are many instances where therapeutic elements must be positioned adjacent to body tissue. One instance involves the formation of therapeutic lesions to the treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia. Therapeutic lesions may also be used to treat conditions in other regions of the body including, but not limited to, the prostate, liver, brain, gall bladder, uterus and other solid organs. Typically, the lesions are formed by ablating tissue with one or more electrodes. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. The tissue coagulation energy is typically supplied and controlled by an electrosurgical unit (“ESU”) during the therapeutic procedure. The amount of power required to coagulate tissue ranges from 5 to 150 W.
A variety of different electrophysiology and electrosurgical devices have been developed for positioning one or more therapeutic elements at the target location. Such devices include catheters, surgical probes and clamps. Although catheters, surgical probes and clamps have proven to be of considerable utility in a wide range of therapeutic procedures, the present inventor has determined that these devices are not well suited for all situations.
In the context of the treatment of atrial fibrillation, for example, conventional electrophysiology and electrosurgical devices have been used to form a set of three transmural encircling lesions that cures paroxysmal atrial fibrillation in most patients. An “encircling lesion,” as used herein, is a lesion that extends around a body structure and is not necessarily circular in shape. The lesion set that typically cures paroxysmal atrial fibrillation includes an encircling lesion around the right pulmonary vein pair, an encircling lesion around the left pulmonary vein pair and an encircling lesion around the left atrial appendage. Additional lesions are frequently required for patients with persistent or permanent atrial fibrillation. A transmural “connecting” lesion that connects the lesion around the right pulmonary vein pair to the lesion around the left pulmonary vein pair may be required if these lesions do not overlap, and a transmural connecting lesion that connects the lesion around the left pulmonary vein pair to the lesion around the left atrial appendage may be required if these lesions do not overlap. Finally, a transmural lesion that extends from the mitral valve annulus to one of the lesions described above, must also be formed.
There are many instances where it is desirable to form lesions epicardially, which involves forming the lesions on the outer surface of the heart, in order to avoid catheter based endocardial procedures and more invasive endocardial surgical procedures. Here, conventional electrosurgical clamps may be used to form the epicardial encircling lesions and conventional electrosurgical probes may be used to form the epicardial connecting lesions. With respect to the lesion that extends from the mitral valve annulus to one of the encircling or connecting lesions, the target left atrial tissue is not accessible from the epicardial surface and the present inventor has determined that conventional electrosurgical apparatus and methods are unable to form this lesion from the outer surface of the heart.